RU2808865C1 - Aerodynamic profile of aircraft lifting element - Google Patents

Abstract

FIELD: aircraft engineering.

SUBSTANCE: aerodynamic profile of the load-bearing element includes upper and lower contours formed by convex curves and their intersection points with given coordinates relative to the profile chord, and has a rounded leading edge.

EFFECT: improved aerodynamic characteristics of profiles for the middle and butt sections of propeller blades, improved flight data of the aircraft in hovering and forward flight, an acceptable low level of variable and constant loads in the load-bearing system, and aeroelastic stability in a wide range of flight speeds are achieved.

4 cl, 6 dwg, 1 tbl

Description

Field of technology to which the invention relates

The invention relates to the field of aircraft construction, in particular, to an aerodynamic profile for the middle and butt sections of the main rotor blades and tail rotor of an aircraft.

The NCV-1 aerodynamic profile of the aircraft's load-bearing element, like other known profiles for similar purposes, consists of the contours of the upper and lower surfaces, described by a set of their geometric coordinates.

From the geometry of the upper and lower surfaces of the airfoil, i.e. the shape of the contour determines the nature of its flow, i.e. the distribution of pressure and air speed over these surfaces and, accordingly, the distribution of aerodynamic forces and moments arising on the airfoil as it flows around it. Thus, the shape of the profile contour determines its aerodynamic characteristics when flowing around with air flow.

The main aerodynamic characteristics of airfoils, namely the coefficient of maximum lift force, the coefficient of minimum drag, the value of the maximum lift-to-drag ratio, the pitching moment coefficient at zero lift, the position of the aerodynamic focus, have a significant impact on the maximum load-bearing capacity of the propeller and on its power consumption in various modes flight, on the level of loads in the control system and the stability of the movement of the blades during propeller operation.

State of the art

The aerodynamic configuration of a rotorcraft blade with high quality and low noise level is known (CN 101541634 B, B64C 27/467, published July 17, 2013). The cross section of this blade includes a rear convexity. The difference between the cross-sectional chord line and the cross-sectional camber line increases from the leading edge of the cross-section to a maximum between the trailing edge of the cross-section and the middle of the chord line and decreases towards the trailing edge, forming the trailing camber of the blade. The rear camber creates more lift with less drag and slows stall at high Mach numbers.

A helicopter tail rotor blade is known (CN 101585413 A, B64C 27/32, B64C 27/467, B64C 27/473, published November 25, 2009), having leading and trailing edges located opposite each other and elongated along the longitudinal axis of the blade; the specially shaped trailing edge interacts with the air flow when the propeller rotates; the blade also has a tip, the chord length of which at the end part decreases from the initial section to the outer one in the radial direction.

The aerodynamic profile of the blade for the main rotor of an aircraft and the main rotor blade with this profile are known (CN 1253532 A, B64C 11/18; B64C 27/467, published 05/17/2000). The profile of this blade includes the upper and lower surfaces between the leading and trailing edges, in which the geometric location of points equidistant from them determines the center line of the profile. In this case, the value of the ratio of the maximum concavity of the center line to the maximum thickness varies linearly with the relative thickness of the profile and is 0.13-0.19 for a relative profile thickness of 7% (from the chord) and 0.18-0.24 for a relative profile thickness of 15% (from the chord). The resulting profile provides increased rotor performance at low lift values and high Mach numbers.

A family of airfoils is known for the blades of rotary-wing aircraft, such as helicopters, and their propellers (US 4412664 A, B64C 27/467, published 01.11.1983). The distribution of the thickness and curvature of these profiles along the chord provides a close to zero pitch moment coefficient in a wide range of lift coefficients and a zero pitch moment coefficient at section Mach numbers of about 0.80, which leads to improved aeroelastic stability characteristics of the aircraft.

The mentioned aerodynamic profiles do not provide an optimal combination of aerodynamic characteristics and have a specific application in the model range of aircraft to solve a certain limited range of problems.

The asymmetrical profiles of the NACA230XX series with a five-digit digital designation, accepted as a prototype, are known, where the last two digits XX are the maximum relative thickness of the profile as a percentage of its chord (see, for example, NACA Report No. 586, 1937, p. 236; Kravets A.S. , Characteristics of aviation profiles, M.-L.: Oborongiz, 1939, pp. 206-217; Ushakov B.A. et al., Atlas of aerodynamic characteristics of wing profiles, M: BIT NKAP at TsAGI, 1940, pp. 165-196 ; NACA Report No. 824, 1945, pp. 101, 146-150). These profiles are widely used in the design of helicopter blades.

The NACA230XX series airfoils have an elongated teardrop shape with a rounded leading edge, a pointed or blunt trailing edge, which are connected by sections of the contours of the upper and lower surfaces of the profile. The contours of these profiles are formed by continuous smooth lines with smoothly varying curvature by superimposing the contours of symmetrical profiles (of appropriate thickness) on the middle line (normal to it), which is constant for the entire series of profiles. The maximum relative thickness of a series of profiles is located at 30% of the profile chord length, and the center line has a maximum relative concavity of 2% (along the axial arc) and is located at 15% of the profile chord length. The contour shape of the prototype NACA23012 profile thus obtained determines its aerodynamic characteristics when flowing around with air flow.

The disadvantages of the NACA23012 profile are:

- relatively high values of the minimum drag coefficient of the profile;

- low values of aerodynamic quality in the Mach number range from 0.4 to 0.7;

- relatively high values of the pitch moment coefficient at zero airfoil lift;

- variable position of the aerodynamic focus of the profile according to the Mach number values.

Disclosure of the invention

The technical problem solved by the invention is to develop the geometry of the upper and lower surfaces of the contours of the NCV-1 aerodynamic profile of the aircraft's load-bearing element (hereinafter referred to as the profile) for the middle and butt sections of the blades, which:

- has large values of the maximum lift coefficient _{Суа max} in the range of Mach numbers from 0.45 to 0.7 compared to the prototype;

- has lower values of the minimum drag coefficient C _{xa min} in the Mach number range from 0.3 to 0.7 compared to the prototype;

- has large values of the maximum aerodynamic quality K _max in the range of Mach numbers from 0.4 to 0.7 compared to the prototype;

- has a smaller absolute value of the pitch moment coefficient C _mo at zero lift in the range of Mach numbers from 0.3 to 0.65 compared to the prototype;

- has a more rearward aerodynamic focus position in the range of Mach numbers from 0.3 to 0.8 compared to the prototype.

The indicated aerodynamic characteristics of the profiles have a major impact on the power consumed by the main and tail rotors, on the level of loads on the structural elements in the booster control part, on the maximum load-bearing capacity, efficiency and movement parameters of the main rotor blades, tail rotor and other load-bearing surfaces of the aircraft.

The technical result of the application of the invention is to improve the basic aerodynamic characteristics of profiles for the middle and butt sections of propeller blades through the use of a developed profile contour that ensures the highest possible quality of the blade and propeller as a whole, both in hovering modes and in forward flight, an acceptable low level of variables and constant loads in the supporting system, as well as aeroelastic stability over a wide range of flight speeds.

To achieve a technical result, an aerodynamic profile of the aircraft's load-bearing element is proposed, including upper and lower contours formed by convex curves and their intersection points with given coordinates relative to the profile chord, having a rounded leading edge, and the relative coordinates of the contour lines , profiles located from the leading edge at relative distances , for a given chord length and maximum relative profile thickness are determined by relations (1), (2):

Where:

- relative abscissa of profile contour points, %;

- relative ordinate of the points of the upper line of the profile contour, %;

- relative ordinate of the points of the bottom line of the profile contour, %;

- relative ordinate of the profile centerline points, %;

- relative ordinate of the points of the symmetrical component of the upper and lower contours of the profile, %;

- maximum relative profile thickness, %;

C _MAX - maximum profile thickness, m;

X - abscissa of profile points, m;

Y _B - ordinate of points of the upper line of the profile contour, m;

Y _H - ordinate of points of the bottom line of the profile contour, m;

B - profile chord length, m,

in this case, the values of the ordinates related to the length of the chord B of the profile , , located from the leading edge at distances , defining the range of ordinates , for maximum relative profile thickness =10% are given below:

In addition, the maximum relative profile thickness ranges from 8 to 20%.

In this case, the aerodynamic profile of the aircraft's load-bearing element may have a pointed, blunt or rounded trailing edge.

In addition, the aerodynamic profile of the aircraft's load-bearing element allows the installation behind the trailing edge of the profile of a tail trimmer plate having a cross-sectional shape of a rectangle or trapezoid, including a curved one, with a length of no more than 15% of the profile chord without a plate, and a thickness of no more than 1.5% profile chord, the bend angle of which relative to the profile chord is in the range from -5° to +10°.

Thus, the technical result of the application of the invention is achieved - improvement of the basic aerodynamic characteristics of profiles for the middle and butt sections of propeller blades, through the use of a developed profile contour that ensures the highest possible quality of the blade and propeller as a whole, both in hovering modes and in forward flight, an acceptable low level of variable and constant loads in the load-bearing system, as well as aeroelastic stability in a wide range of flight speeds. The use of the proposed profile makes it possible to improve the flight performance and economic characteristics, expand the scope of application and increase the competitiveness of the aircraft.

Brief description of drawings

The invention is illustrated by drawings:

Fig. 1 - Variant of the profile contour and graphs of the geometric characteristics of the profile as a percentage of the length of the profile chord for the maximum relative thickness =10%.

Fig. 2 - Graphs of the dependences of the coefficients of maximum lift force C _{yа max of} the compared profiles on the Mach number.

Fig. 3 - Graphs of the minimum drag coefficients C _{xa min of} the compared profiles versus the Mach number.

Fig. 4 - Graphs of the dependences of the maximum aerodynamic quality K _max of the compared profiles on the Mach number.

Fig. 5 - Graphs of the dependences of the coefficients of the pitching moment, determined relative to the leading edge of the airfoil, C _m0 at zero lift of the compared airfoils on the Mach number.

Fig. 6 - Graphs of the relative coordinates of the aerodynamic focus compared profiles on the Mach number.

Carrying out the invention

The proposed profile has a rounded leading edge, a pointed, blunt or rounded trailing edge, interconnected by smooth contours of the upper and lower surfaces of the profile, the leading edge is made with a rounding radius that smoothly increases along the profile chord of length B so that the distance Y _B from the profile chord normal to it up to the top of the contour gradually increases from the leading edge of the profile and in the range of coordinates along the chord X = 0.3 ⋅ V - 0.4 ⋅ V reaches its maximum value, the upper part of the contour smoothly passes from convex to concave. The front edge of the lower surface of the profile is made rounded with a radius of curvature along the lower part of the contour. The distance Y _H from the profile chord to its lower surface gradually increases from the leading edge and reaches its maximum value at X = 0.6 ⋅ V - 0.8 ⋅ V.

The proposed profile refers to the middle and butt sections of the blade and includes the upper and lower contours formed by convex curves and their intersection points with given coordinates relative to the profile chord. The coordinates of convex curves are measured from the profile midline: the upper one is added, the lower one is subtracted.

Relative coordinates of contour lines , profiles located from the leading edge at relative distances , for a given chord length and maximum relative profile thickness are determined by relations (1), (2):

Where:

- relative abscissa of profile contour points, %;

- relative ordinate of the points of the upper line of the profile contour, %;

- relative ordinate of the points of the bottom line of the profile contour, %;

- relative ordinate of the profile centerline points, %;

- relative ordinate of the points of the symmetrical component of the upper and lower contours of the profile, %;

- maximum relative profile thickness, %;

C _MAX - maximum profile thickness, m;

X - abscissa of profile points, m;

Y _B - ordinate of points of the upper line of the profile contour, m;

Y _H - ordinate of points of the bottom line of the profile contour, m;

B is the length of the profile chord, m.

Table 1 (in the first, second and third columns) shows the values of the relative abscissas of the profile contour points and the corresponding relative ordinates of the profile centerline points and ranges of ordinates of points of the symmetrical component of the upper and lower contours of the profile . Calculation of ranges of relative ordinates of points of the upper and lower line of the profile contour is fulfilled according to relations (1), (2), respectively. Calculation example for a given maximum relative profile thickness =10% is given in Table 1 (in the fourth and fifth columns).

The dimensions of the values C _MAX , X, Y _B , Y _H , B, when constructing a profile, can be selected not only in meters, but also in other units of length.

It is possible to construct the coordinates of a series of profiles of various thicknesses. At the same time, the values , in table 1 remain unchanged, and the values are calculated according to relations (1), (2) respectively for the maximum relative thickness of the profile set in the range from 8 to 20%.

Dimensional values X, Y _SR , Y _SIM , Y _B , Y _H are obtained by multiplying the relative values to a given dimensional value B of the profile chord length.

The geometric shape of the profile contour (Fig. 1) determines its aerodynamic characteristics when flowing around with air flow. The aerodynamic characteristics of the proposed profile, obtained by computational fluid dynamics methods, are illustrated in graphs (Fig. 2-6) in comparison with the characteristics of the prototype NACA23012 profile. In the graphs, the dotted line indicates the characteristics of the prototype NACA23012 profile, and the solid line indicates the characteristics of the proposed profile.

In fig. Figure 1 shows a variant of the profile contour and graphs of the geometric characteristics of the profile as a percentage of the profile chord length for the maximum relative thickness =10%, where:

Y _CP - ordinate of the profile center line points;

Y _SIM - ordinate of the points of the symmetrical component of the upper and lower contours of the profile;

Y _B - ordinate of the points of the upper line of the profile contour;

Y _H - ordinate of points of the bottom line of the profile contour;

B is the length of the profile chord;

- maximum relative profile thickness, %;

- relative abscissa of profile contour points, %;

- relative ordinate of profile contour points, %;

- relative ordinate of the profile centerline points, %;

- relative ordinate of the points of the symmetrical component of the upper and lower contours of the profile, %.

In fig. Figure 2 shows graphs of the maximum lift coefficients C _{yа max} of the compared profiles as a function of the Mach number. The proposed profile is superior to the NACA23012 profile in terms of maximum lift at Mach numbers above 0.45.

In fig. Figure 3 shows graphs of the minimum drag coefficients C _{x min} of the compared profiles as a function of the Mach number. The minimum drag of the proposed profile is lower than the minimum drag of the NACA23012 profile, in the range of Mach numbers from 0.3 to 0.7 by an average of 12%.

In fig. Figure 4 shows graphs of the dependences of the maximum aerodynamic quality _Kmax of the compared profiles on the Mach number. The values of the maximum aerodynamic quality of the proposed profile are higher than those of the NACA23012 profile, in the range of Mach numbers from 0.4 to 0.7 by an average of 24%.

In fig. Figure 5 shows graphs of the dependences of the coefficients of the pitching moment determined relative to the leading edge of the airfoil, C _t o at zero lift of the compared airfoils on the Mach number. The proposed airfoil has lower zero-lift pitching moment values than the NACA23012 airfoil in the Mach number range of 0.3 to 0.65.

In fig. 6 shows graphs of the relative coordinates of the aerodynamic focus compared profiles on the Mach number. The proposed profile has a more rearward focus position than the NACA23012 profile, in the Mach number range from 0.3 to 0.8, which improves the aeroelastic stability of the blade motion over a wide range of flight speeds.

Thus, the proposed aerodynamic profile NTsV-1 of the load-bearing element of the aircraft, designed in accordance with the essence of this invention, has, in comparison with the prototype profile NACA23012, advantages in the main aerodynamic characteristics in certain ranges of Mach numbers, namely, it exceeds the maximum lift force, The drag is reduced, the values of the maximum lift-to-drag ratio are increased, lower values of the pitching moment are achieved at zero lift, and the aeroelastic stability of the movement of the blades is increased in a wide range of flight speeds.

The proposed aerodynamic profile of the aircraft's load-bearing element allows the installation behind the trailing edge of the profile of a tail trimmer plate having a cross-sectional shape of a rectangle or trapezoid, including a curved one, with a length of no more than 15% of the profile chord without a plate, and a thickness of no more than 1.5% of the profile chord , the bend angle of which relative to the profile chord is in the range from -5° to +10°.

In the production of blades using the developed family of aerodynamic profiles, it is planned to use modern materials and technologies.

Claims (20)

1. An aerodynamic profile of the supporting element of an aircraft, including upper and lower contours formed by convex curves and points of their intersections with given coordinates relative to the chord of the profile, having a rounded leading edge, characterized in that the relative coordinates of the convex curves , profiles located from the leading edge at relative distances , are measured from the profile centerline for a given chord length and maximum relative profile thickness and are determined by relations (1), (2) Where - relative abscissa of profile contour points, %; - relative ordinate of the points of the upper line of the profile contour, %; - relative ordinate of the points of the bottom line of the profile contour, %; - relative ordinate of the profile centerline points, %; - relative ordinate of the points of the symmetrical component of the upper and lower contours of the profile, %; - maximum relative profile thickness, %; C _MAX - maximum profile thickness, m; X - abscissa of profile points, m; Y _B - ordinate of points of the upper line of the profile contour, m; Y _H - ordinate of points of the bottom line of the profile contour, m; B - profile chord length, m, in this case, the values of the ordinates related to the length of the chord B of the profile , , located from the leading edge at distances , defining the range of ordinates , for maximum relative profile thickness =10%, given below 2. The aerodynamic profile of the supporting element of the aircraft according to claim 1, characterized in that the maximum relative thickness of the profile ranges from 8 to 20%. 3. The aerodynamic profile of the supporting element of the aircraft according to any one of paragraphs. 1 and 2, characterized in that it may have a pointed, blunt or rounded rear edge. 4. The aerodynamic profile of the supporting element of the aircraft according to any one of paragraphs. 1-3, characterized in that it allows installation behind the trailing edge of the profile of a tail trimmer plate having a cross-sectional shape of a rectangle or trapezoid, including curved, with a length of no more than 15% of the profile chord without a plate, with a thickness of no more than 1.5% of the chord profile, the bend angle of which relative to the profile chord is in the range from -5° to +10°.